Abstract

Atrial septal pouch is a common anatomic variant of the interatrial septum and a nidus for thrombus formation. Left-sided atrial septal pouch has been associated with an increased risk of cryptogenic stroke. We described a case of left-sided atrial septal pouch thrombus, incidentally found prior to transseptal puncture during Watchman device placement. This case highlights the importance of a thorough echocardiographic evaluation of the atrial septum prior to transseptal access and recognition of this finding as a potential cardiac source of embolism.